The cell's mitochronrion need oxygen to produce ATP using glucose.
celluse
Cellulase is an enzyme that break down celluse a complex organic molecule into simpler molecule like glucose and as such being an enzyme, it is also protein in nature.
plants make food from the process of photosynthesis. through this, plants take in light energy from the sun along with CO2 from animals respiratory waste, to store into mechanisms they have called chloryphyll/chloroplasts. From there, plants can make compound sugars; glucose used to nourish plants, and cellulose used as the plants protective "skin" outercoating. only glycogen is edible for humans, whereas celluse is too complex for our bodies to completely break down into simpler substances.